This invention relates to an improved process for the effective minimization of waste materials while recovering therefrom an optimized proportion of fuel components and other useful products. The improved process of this invention employs both pyrolysis and gasification to achieve an environmentally desirable result.
Pollution of the environment has become a major problem in recent years and has now reached a state where conventional procedures for handling typical wastes are no longer adequate or even permissible. Increased concern for both working and living conditions has led to the enactment and enforcement of legislation intended, in part, to require disposal of waste materials, including harmful or hazardous waste materials, without causing additional pollution of the environment. Landfills are rapidly reaching the limits of their capacities and the generally suggested and preferred means for future processing usually involves incineration.
Major types of waste materials include a great variety of industrial wastes; municipal wastes and related sanitary wastes; hazardous wastes, including infectious wastes from hospitals; marine wastes; and agricultural wastes.
Typical hazardous waste materials include oily liquids such as polychlorinated biphenyls as well as various solid pesticide formulations and by-products such as dioxins as well as hospital wastes. Incineration has been practiced at sea as well as in various land-based operations. The latter include the co-firing of hazardous wastes in high-temperature industrial processes employing, for example, steel furnaces, cement kilns, lime kilns, and glass melting furnaces.
The complete incineration of waste material may be effected in a sub-surface cavity, as described in U.S. Pat. No. 4,438,708, either underground or under water. Liquid oxygen is supplied in excess so that ignition leads to complete destruction of the combustible material. Similarly, U.S. Pat. No. 4,077,337 relates to combustion of wastes in a closed room, employing pure oxygen to assure complete reaction. Waste coal in an abandoned mine may be combusted, as in U.S. Pat. No. 4,387,655, in a stream of air, with recovery of heat energy. Earlier art, relative to underground burning, includes various techniques for burning stumps, as, for example, U.S. Pat. Nos. 1,141,747; 1,190,006; 1,440,741; and 1,617,867.
U.S. Pat. No. 3,658,015 describes a submerged incinerator for burning oil residues from drill cuttings at an off-shore well-drilling location.
A portable incinerator is disclosed in U.S. Pat. No. 3,452,690, whereby radioactive waste is burned in a three-tier combustion assembly which can be placed over an ash pit.
In U.S. Pat. No. 3,768,424, solid waste material is pyrolyzed by heating in the absence of air at an unspecified temperature. Vaporized materials are then burned in air in the presence of a combustible gas such as propane.
In U.S. Pat. No. 4,253,406, pollution control is effected with a flueless combustion chamber wherein gaseous combustion products are diverted downwardly and finally through a standpipe. The combustion unit and downstream equipment are portable and can be used with part of the installation situated below grade.
U.S. Pat. No. 4,279,208 provides a method and apparatus for incineration of industrial wastes wherein the oxygen content of the combustion mixture is regulated by varying the feed rate of either air or pure oxygen, in a dual feed system, in response to a feedback signal indicating a parameter characteristic of the flue gas streams. In this manner, a selected oxygen content and a combustion temperature may be maintained.
In a gaseous combustion system, U.S. Pat. No. 4,038,032 provides for feedback control signals to regulate the proportion of combustible waste gas in the feed in order to avoid the presence of an explosive mixture.
Such combustion techniques typically create large additional quantities of carbon oxides, particularly carbon dioxide, which are discharged to an already polluted atmosphere. The typical oxidizing agent is air and, at typical combustion temperatures, the formation of various nitrogen oxides creates an additional pollution problem. All of this contributes in a major way to the worsening of the so-called "greenhouse effect" which threatens permanent deterioration of the environment.
Accordingly, there exists a serious need for the provision of improved waste processing methods which have the added advantage of generally improving the environment.